It's done with all sorts of meat, including chicken. It's used mostly with thicker cuts of meat.
There are a number of reasons to allow meat to rest before serving. One is to give the heat a chance to even out. For a thick roast, the outside gets hit with the direct heat from the oven, and the inside only gets what is conducted from the outside. If you let it cook until the inside reaches the right temperature, the outside will be overcooked. So instead, we pull it out of the oven a bit early, and let the hot outside continue to cook the inside.
The other reason is that it allows the meat to reabsorb its juices. As the proteins denature, the juice is squeezed out of the cells, and it's pushed towards the outside of a thick piece of meat. If you slice it, the juices will leak out. If you allow it to rest first, the juices gradually reabsorb throughout the meat, making it tastier.
There will usually be some squeezed out juices anyway, no matter what you do. To keep the flavor these are often added to the pan and turned into a sauce. But the meat is tastier and more tender if the juices are still in the meat rather than poured on top.
Many chefs allow a thick roast to rest even longer. For big roasts I've seen resting times as much as a half-hour.
Chefs are increasingly turning to a different kind of roasting. Chef Herve This is the leader in this field. He makes roast beef by roasting it at only 180 degrees for as much as three hours a pound. Cooked that slowly, the juices never get squeezed to the outside, and remain right where they are. It makes a very tender and juicy piece of meat. And so what if it takes all day?